Looking for some suggestions on which apartment rental agencies to use and which to stay away from. Any experience with Rental in Rome?

You will find good recommendations for www.sleepinitaly.com here

I haven't worked with Rental In Rome, but during my research I saw a lot of very negative feedback for them (switching to a more expensive on arrival without compensation, etc.). I am working with realrome.com, and so far the interactions have been very positive.

I used www.rentalinrome.com a couple of weeks ago with no problems at all. I worked with Anna and she was great. They are a company which represents hundreds of apartments. I read the negative comments too, but no company is perfect. The apartment we chose was the best fit for us and everything worked out perfectly.
If you click on my name, you will see my current trip report which included comments about the apartment and a link to photos.

I used Rental in Rome last Sept. No problems at all.

We used realrome.com and found the owner, Tim Pearson, wonderful to work with. The agency gets consistently good reviews here and on trip advisor.